APPLICATION OF PROTOPLAST FUSION TO CITRUS BREEDING

Protoplast fusion in higher plants is a useful technique for production of novel plants which cannot be obtained by conventional breeding methods. For more than a decade, successful somatic hybridization was limited to herbaceous plants. In Citrus, the use of nucellar callus obtained from ovules, possessing high regeneration ability, made it possible to regenerate whole plants from protoplasts. Then, somatic hybridization in the Rutaceae family was established, and many intergeneric or interspecific amphidiploid somatic hybrid plants were produced. Recently developed molecular biology techniques have provided more direct methods for the identification of somatic hybrids in both the nucleus and cytoplasm, and the results are expected to provide useful information about nuclear-cytoplasmic interaction. Some somatic hybrids have flowered and produced fruit, and their male and female fertility has been confirmed. Somatic hybridization in Citrus will undoubtedly be a useful technique for overcoming barriers of sexual hybridization and for improving Citrus scion and rootstock.